1. Field of the Invention
The present invention relates to a method for determining the reference phase in a radio communication system that uses orthogonal M-ary modulation, and a coherent detection method that uses the same.
2. Description of the Related Art
Code division multiple access (CDMA) systems are gaining attention as next-generation mobile communication systems, and a standard system, called IS-95, already exists in the United States. As means of infrastructure building, CDMA systems based on a semi-fixed mobile communication system called a wireless local loop (WLL) could also be put to use.
This is a CDMA system with a chip rate of 1.2288 Mcps proposed by Qualcomm, Inc. of the United States, the downlink of which uses a coherent detection system, which utilizes a pilot extrapolation signal. Conversely, the uplink uses an non-coherent detection system, which utilizes orthogonal M-ary modulation.
As for the non-coherent detection system, which uses orthogonal M-ary modulation in the uplink in this IS-95 standard system, by converting the amplitude signal to power at the receiving end, phase errors caused by fading and the like are removed to prevent degradation. However, error rate characteristics deteriorate more during non-coherent detection than during coherent detection.